1. Field of the Invention
The present invention relates to an endoscope light source unit suitable for an endoscope, or an electronic endoscope, etc.
2. Description of the Related Art
Recent electronic endoscope systems have a processor with a built-in light source unit, to which an electronic scope having an electronic camera mounted on the distal end thereof or a fiber scope for conducting observation only through optical members is connected for use. In particular, electronic scopes have been provided for use with a wide variety of thicknesses and functions suited to different locations of observation. Processors connectable with various types of electronic scopes and fiber scopes must also have light source units that are compatible with such various electronic scopes and fiber scopes. For this reason, conventional light source units have been constructed so as to supply necessary amounts of light to electronic scopes that require maximum light intensities.
Such light source units are configured such that illumination light emitted from a high-intensity lamp is condensed by a condenser lens and made incident on the incident end face of a scope light guide, typically an optical fiber bundle. Since the necessary amount of illumination light varies with the type of electronic scope and with the observation location, the light source units are equipped with an aperture device for adjusting the amount of light mechanically. Among known aperture devices is one that includes a diaphragm which is composed of a partly-notched portion and an arm portion integrated with the partly-notched portion, having such a size that all the light from a light source lamp can be blocked; and a motor mechanically connected to an end of the arm portion. The motor is rotated to turn the diaphragm about the top of the arm portion, thereby adjusting the illumination intensity (see Japanese Patent Laid-Open Publication No. 2003-305008). Moreover, a light shielding plate may be provided with a plurality of aperture openings having different opening ratios or transmittances so as to form a rotary aperture plate which regulates the amount of light incident on the incident end face of a light guide by putting one of the aperture openings selectively between a light source unit and the incident end face of the scope light guide (i.e., into the illumination optical path). This rotary aperture plate is moved into the illumination light path at an aperture opening having an opening ratio (transmittance) corresponding to the scope.
As with the conventional aperture devices, the rotary aperture plate is driven with an open control and a relative rotation measurement which measures the driving amount for the rotary diaphragm plate to be driven from the initial position. The open-control driving, however, has a disadvantage that the rotary aperture plate can easily cause a shift in position due to vibration and impact. If the rotary aperture plate is continued to be used with a shift in position, aperture openings having opening ratios higher than an allowed opening ratio for the scope may be undesirably moved into the illumination optical path during use.